1. Field of the Invention
The present invention relates generally to controls for fuel injection systems for internal combustion engines. More specifically, the invention relates to a timing control for regulating injection timing in fuel injectors for compression ignition type internal combustion engines, especially wherein fuel is supplied to unit fuel injectors which operate on a pressure-time metering principle via a hydromechanical fuel system.
2. Background Art
Unit fuel injectors which operate on a pressure-time metering principle have been in use for some time now (see U.S. Pat. Nos. 4,721,247; 4,986,472 and the patents mentioned therein), and have contributed greatly to the ability of internal combustion engine designers to meet the ever increasing demands for improved pollution control and increased fuel economy. In fuel supply systems using such injectors, fuel is supplied by a gear pump to all of the injectors via a fuel rail and the same is true for timing fluid used to control the degree that the timing of the injection event is advanced or retarded, with the quantity of fuel and timing fluid delivered to each injector being a function of the supply pressure from the common rail and the time period during which the metering and timing chambers are in communication with the respective supply rails. Examples of gear pump type fuel supply systems for P-T type unit fuel injectors can be found in U.S. Pat. Nos. 4,909,219 and 5,042,445 as well as in Cummins Engine Company's Bulletin No. 337929401 which illustrates a PT type H automatic fuel controller.
However, for the continuing demands for improved pollution control and increased fuel economy to be met, it becomes increasingly essential to be able to optimize the combustion process, not only by precisely controlling the quantity of fuel injected into each cylinder, but also by precisely regulating the timing thereof, and this has become increasingly more difficult as the level of combustion efficiency to be obtained is raised. Ultimately, increased precision means that the controller must be infinitely variable as well as responsive to the various parameters affecting fuel quantity and timing.
U.S. Pat. No. 4,869,219 discloses an air fuel control for P-T fuel systems which uses a diaphragm-type operator to provide a controlled, optimum amount of fuel as a function of intake manifold pressure, and which can be retrofit installed on previously existing engines. However, no equivalent control for regulating engine timing is provided.
U.S. Pat. Nos. 3,486,492 and 4,408,591 show fuel injection pumps which have a built-in timing control which can delay advancing of injection timing upon acceleration. However, these disclosures relate to distributor-type pumps not gear pumps, and are not adapted to the needs of P-T fuel injectors and the fuel systems therefor. Likewise, U.S. Pat. No. 3,598,097 discloses a hydraulic regulator system for fuel injection pumps in which a pressure control valve is provided having a spring-loaded piston which responds to changes in the pressure of fuel supplied from a gear pump to adjust the flow of the fuel which acts on an injection timer setting member by varying the extent to which a port is block and unblocked by the spring-loaded piston. However, this system does not control timing fluid flow as a function of pressure in a metering rail for supplying fuel for injection, and in general, also, is not adapted to the needs of P-T fuel injectors and the fuel systems therefor.
In commonly owned, U.S. patent application Ser. No. 08/007,973, now U.S. Pat. No. 5,277,162, an infinitely variable hydromechanical timing valve that can precisely regulate engine timing as a function of engine speed and load conditions is described. This timing valve is a spool-type hydromechanical timing valve and is provided with a valve body assembly having a barrel and plunger arrangement. The plunger is displaceable within the barrel under the counterbalancing forces of rail fuel pressure (load) and one or more timing valve springs. The relative position of the barrel and plunger determines the effective size of the port through which timing fluid can flow. For example, in accordance with a first embodiment, the plunger has a tapered head which covers and uncovers ports in the barrel to a greater or lesser extent, thereby creating a variable flow-through cross section. Alternatively, in accordance with other embodiments, the barrel has ports with slot-like orifices of progressively changing widths which coact with a metering groove on the plunger to define a variable flow cross section through which the timing fluid must pass.
While the system of this prior application has many advantages, it has many critical dimensions due to the complex shape of the metering port and metering groove plunger. Furthermore, such a system would likely require a family of assemblies to address a wide range of engine types and ratings. This is because the port and reference springs produce a valve restriction that is a particular function of rail pressure, and a function that is appropriate for one engine application is easily inappropriate for a widely different engine application.